It verifies all the behavior that you tell it to. Consider the simple example used to help teach people to use type systems effectively: tic tac toe. You can

It verifies all the behavior that you tell it to. Consider the simple example used to help teach people to use type systems effectively: tic tac toe. You can write an implementation of tic tac toe in which the behavior of the game is type checked. You can even do so in java, although it is certainly more effort than in a more powerful language.